In a wireless local area network (WLAN), a mechanism must exist for enabling a wireless station (STA) to discover a wireless access point (AP).
In one known technique, a wireless station waits to receive a beacon transmission originated by an access point. Such a beacon may be transmitted by the access point on a periodic basis, such as once every 100 ms. This technique is referred to in the art as passive scanning. The wireless station may respond to the beacon by making connection with the access point.
In another known technique, the wireless station sends a probe request out into the network and then waits to receive a response from an access point that detects that probe request. This technique is referred to in the art as active scanning. The wireless station may then respond to the probe request response by making connection with the responding access point.
As general rule, discovery of the access point by the wireless station is accomplished more quickly with active scanning than with passive scanning. There are, however, concerns with the use of the active scanning technique. One problem with active scanning is that the probe request is transmitted by the wireless station in a broadcast mode, and this may prompt multiple probe request responses from multiple listening access points. Access may be delayed as the wireless station must decide on making a connection between several responding access points. In the situation where a plurality of wireless stations need to associate with a single access point, the transmission of probe requests by each one of the multiple wireless stations may flood the network and adversely delay achieving discovery of and connection to the access point. Further, active scanning consumes more power than passive scanning, which may not be suitable for wireless stations (such as mobile devices) where battery consumption is of critical concern.
To better support the passive scanning mode, it is known in the art to have the access points send beacons more frequently. This solution, however, has the drawback that the more frequently transmitted access point beacon communications will occupy substantial air time. Furthermore, it is understood that in the situation where a plurality of wireless stations need to associate with a single access point, the time spent by those wireless stations in passively waiting for a beacon transmission from the access point leads to inefficient wireless network operation.
To address the foregoing and other concerns, the IEEE 802.11ai standard proposes the use of a fast initial link setup (FILS) discovery beacon broadcast by access points for enabling access point discovery by wireless stations. The FILS discovery beacon may be a frame or packet. The terms FILS discovery beacon and FILS discovery frame are used herein interchangeably. Wireless stations discover an access point by detecting a FILS discovery beacon transmitted repeatedly from the access point at shorter or faster subsequent time intervals (e.g., higher frequency) than a typical beacon, which is typically transmitted at a period of 100 ms or other frequency according to IEEE 802.11 standards. The FILS discovery beacon may be transmitted with the standard or typical beacon. However, the FILS discovery beacon has a modified format that comprises less information than a typical beacon format. The reduced size of the FILS discovery beacon in comparison to a typical or regular transmitted beacon avoids the problem identified above concerning the occupation of substantial air time by the beacon broadcasts. The faster transmission time interval and the smaller size format of the FILS discovery beacon are implemented to speed up the access point discovery process. The goal is to achieve a FILS total association time requirement (beacon detection and association between the access point and a wireless station) of about 100 ms.
It is also known in the art to transmit the FILS discovery beacon with a randomized broadcast pattern (for example, according to a predefined sequence of transmission and non-transmission phases). The randomized broadcast pattern improves the chances for faster detection of the FILS discovery beacon and avoids a broadcast collision in the case of multiple access points operating in passive mode.
Alternatively, the FILS discovery beacon is transmitted with a periodic broadcast pattern at a relatively higher frequency than with standard beacons and without using any predefined sequence of transmission and non-transmission phases.
Reference is made to United States Patent Application Publication 2013/0177002, the disclosure of which is incorporated by reference, for a discussion of the FILS process.
Those skilled in the art recognize, despite the advantages of the FILS discovery beacon, that the FILS discovery beacon does not harmonize very well with IEEE 802.11ac. Multiple basic service set identification (BSSID) support is not present and 802.11ac capability information is not provided. There is accordingly a need in the art for an improved FILS discovery beacon in support of detection and association between an access point and a wireless station in a wireless communication network.